John Ericsson, Swedish-American naval engineer and inventor, designed the Monitor, the first ship with an armored, revolving gun turret. The Monitor engaged the Confederate Merrimack on March 9, 1862, in the first naval engagement between two ironclad vessels. Ericsson also designed the Princeton, in 1844, the first warship with a screw propeller and with engines below the waterline. After the Civil War he experimented with solar energy, torpedoes, and steam engines.